Balsa Cabinets?

[dnsey]

I was knocking up an experimental HF horn from balsa wood, and it suddenly occured to me that balsa might make a good cabinet material.
Low resonance, intrinsic damping, relatively strong... seems like a possibility.
I know balsa sandwiches have been done, but has anyone tried balsa as the main structure? Obviously finishing might be a problem (fabric of some sort is a possibility), and I don't know what are the largest panels available, but from the illustrations I've seen, the trees can be quite substantial.
Any thoughts?

[DAVOhorn]

Dear dnsey,

try talking to the folks at the de Haviland aeroplane co.

They used marine ply carcass with balsa wood filler to give a true laminate composite material.

When they first came up with this idea for a fighter the MOD laughed loud and long.

They then realised that there was no more metal to make real aeroplanes so went back to de Haviland and asked them to build the funny wooden plane.

So the de Haviland Mosquito came into being.

Very light very strong resilient to damage and easily repaired when damaged.

So if it was good enough to cause havoc in WW2 then why not today as a cabinet material.

Try it and see.

3-6mm ply outer and inner skin with 15mm balsa inner filler.

Should be interesting. Very light and very stiff with good damping properties.

regards David

[Stocker]

Don't use it for bass. Or use it for bass and see if you can make it explode...

Well, use thick panels for bass, good luck getting them though.

I would want to do some experimentation before saying the material doesn't have a resonance in an important audible range.

$0.02

[filgor]

I agree with DAVOhorn. At least as far as strength to weight goes it would be ideal as part of a composite

If you are talking about using it on its own. It has a high strength to weight ratio but you would need to use very thick panels as Stocker mentioned. A broad panel of Balsa will flex quite easily. You could also overcome this by using redioculously extensive internal bracing.

AFAIC the only solid advantage of using balsa for a speaker cabinet it that it is so easy to shape. You can make a sculptured shape out of a solid balsa block using little more than a pen knife and sandpaper.

Besides all this It is actually a good idea to have a cabinet that is reasonably heavy otherwise the divers motor will tend to move the cabinet as well as the air in front of its diaphram!

[sreten]

Hi,

it all sounds fairly reasonable.

Composites are well known and its the outer ~15% of
each surface that counts, mechanical performance of the
other 70% doesn't really matter but for balsa ideally the
grain would run surface to surface, though practically its
best to let the grain run along the length of a panel.

So you get a light, strong and very stiff panel, great !
Which you can then damp for a classic BBC style cabinet.

Worked all this out a long time ago and then looked
at the price of balsa wood. Owwwwcccchhhh!!!!!!!!!

/sreten.

[EC8010]

As sreten says, the strength is in the skin, not the core. An ideal composite would be a skin of the really thin plywood that modellers use with a balsa core. Yes, I found out about the Mosquito too. And I found out how expensive balsa is. On the other hand, the amount of work that you put into making a pair of loudspeakers is so great that I don't consider the material cost to be, well, material.

Little known fact: The Apollo lunar lander used balsa as a shock absorber on the legs.

[owen]

Try this http://www.jamestowndistributors.com...;eclDrill;3249

Ideal as a starting point - thin ply (3 ply or 5 ply) on the exterior and you're good to go - If you laminate with balsa however, you will reduce weight further, and be able to cut using a scalpel (making comstruction more of a kitchen table affair).

I've constructed very small speakers from balsa (in my misspent youth) - they were all charecterised by a very natural 'tone'

I anticipate great results!

Owen

[filgor]

Originally posted by dnsey
I know balsa sandwiches have been done, but has anyone tried balsa as the main structure?

Are you asking if Balsa alone will work? Because everyone is pushing the composite idea for good reason.

Originally posted by EC8010
the amount of work that you put into making a pair of loudspeakers is so great that I don't consider the material cost to be, well, material.

Aint that the truth.

Balsa is also so easy to work that it almost justifies the cost.
(I know this pobably wasn't your point)

I still think the weight of MDF is an advantage. Remember we are talking about a speaker cabinet not an aircraft.
The amount of energy passing to the cabinet from both the driver and its backwave is semi dependent on how light as well as compliant and lossy the material is. A light composite not fair as well unless it really is significanly stiffer.

[owen]

The celestion aerolam speakers are fairly lightweight, and I see no reason why the balsa composite should not be as stiff.

The Aerolam speakers were very highly regarded...

Owen

edit - found the celestion reference

In 1983 the revolution was completed by the addition of an aluminium honeycomb cabinet which provided a remarkably high stiffness/weight ratio. The SL600 set new standards at the audiophile end of the market, selling particularly well in Japan, and winning numerous awards around the world.

from http://www.celestion.com/history/1980s.html

Good enough for Japan, good enough for me!

Owen

[EC8010]

Originally posted by owen
The Aerolam speakers were very highly regarded...

And that from a speaker with some distinctly iffy drivers! (The copper dome tweeter had its first breakup mode within the audio band.)